Increase of engine room temperature, recycle of exhaust gas, and fuel evaporative emission regulation have recently progressed in view of exhaust gas control and energy saving of automobiles, and as a result, it has been required that rubber materials to be used therefor have thermal aging resistance, and resistance to weather, sour gasoline, alcohol-containing gasoline, and low fuel permeation, etc. Rubber materials, which sufficiently satisfy the above properties and can be used in fuel oil hoses, include fluororubbers. However, the fluororubbers are 10 to 20 times more expensive than common rubbers in terms of cost and disadvantageously poor in cold resistance. Thus, laminates having a thin inner layer of a fluororubber and an outer layer of an epichlorohydrin-based rubber have widely been used in the hoses for fuel oils such as gasoline instead of acrylonitrile-butadiene copolymer rubbers (NBR).
In the laminates of the fluororubber layers and epichlorohydrin-based rubber layers, vulcanizing agents for the fluororubbers have been selected from bisphenol-, polyamine-, or organic peroxide-based vulcanizing agents, etc. depending on the purpose of use, and now the use of organic peroxide-based vulcanizing agents is expanding because the fluororubbers using them are excellent in resistance to acid products due to decomposition of fuel oils and amine-based additives contained in the fuel oils.
In the above multilayer rubber hoses, adhesiveness between the different rubber layers is the most important subject. It is known that the fluororubber layer and epichlorohydrin-based rubber layer are poor in the adhesiveness to each other, and thus the rubbers are generally bonded by methods of adding certain additives to the epichlorohydrin-based rubbers or fluororubbers to improve adhesiveness.
Patent Document 1 discloses that adhesiveness is improved by adding, as an epichlorohydrin-based rubber composition, an organic peroxide-based or an amine-based vulcanizing agent and a specific phosphonium salt in a rubber laminate of a fluororubber and an epichlorohydrin-based rubber.
When the epichlorohydrin-based rubber is crosslinked by organic peroxide, ethylene dimethacrylate or the like is blended as a crosslinking aid for the purpose of improving the crosslinking effect. However, there has never been obtained a knowledge in which adhesiveness between the epichlorohydrin-based rubber crosslinked by the organic peroxide and the fluororubber is improved by blending ethylene dimethacrylate. It is known that since sufficient heat resistance of the epichlorohydrin-based rubber is not obtained by crosslinking by the organic peroxide, the addition of ethylene dimethacrylate is not suited for such applications (fuel oil hoses) that heat aging resistance is required.
Patent Document 2 discloses that, in a rubber laminate of a fluororubber and other kinds of rubbers, adhesiveness between the other kinds of rubbers and the rubber laminate is improved by using a composition which is prepared by blending an acrylic rubber obtained by copolymerizing a specific amount of a polyfunctional monomer with a fluororubber.
Patent Document 3 discloses that, in a rubber laminate of a fluororubber and an epichlorohydrin-based rubber, adhesiveness between the layers is improved by mixing a fluororubber containing an organic peroxide-based vulcanizing agent with triallyl isocyanurate, and that crack propagation resistance are improved by mixing ethylene glycol dimethacrylate as one polyfunctional (meth)acrylate compound with triallyl isocyanurate in a specific ratio.
Patent Document 4 proposes, as a method of improving adhesiveness between an epichlorohydrin-based rubber and a fluororubber containing an organic peroxide-based vulcanizing agent, a method of using an epichlorohydrin-based rubber containing 3 to 15 mol % of a constituent unit of allyl glycidyl ether.    Patent Document 1: JP-A-4-372652    Patent Document 2: JP-A-10-536475    Patent Document 3: JP-A-2007-271077    Patent Document 4: JP-A-2006-306053